1. Field of the Invention
The present invention relates to multiphoton-excitation laser scanning microscopes.
This application is based on Japanese Patent Application No. 2007-117074, the content of which is incorporated herein by reference.
2. Description of Related Art
Among known microscopes is a multiphoton-excitation microscope, which uses multiphoton excitation to acquire a bright fluorescence image of a specimen with high resolution in the depth direction (for example, see Japanese Unexamined Patent Application, Publication No. 2006-3521).
To avoid the problem of fluorescence emitted from a specimen as a result of multiphoton excitation being attenuated before being detected by a light detector because of loss caused when it passes through a plurality of optical elements such as mirrors and lenses, the multiphoton-excitation microscope according to Japanese Unexamined Patent Application, Publication No. 2006-3521 includes a light detector disposed at a position reached by the fluorescence after it passes through only an objective lens and a dichroic mirror, thus acquiring a bright multiphoton-excitation fluorescence image with reduced fluorescence loss.
Of the fluorescence emitted from the specimen in all directions, however, the fluorescence collected by the objective lens is limited by the numerical aperture of the objective lens. This poses a problem in that the emitted fluorescence cannot be efficiently detected unless the numerical aperture of the objective lens can be increased. For electrophysiological experiments, for example, in which a needle, as used in a patch clamp, is often inserted near the examination site on a specimen, the tip angle of the objective lens cannot be increased because it would otherwise interfere with the needle. Hence, an objective lens with high numerical aperture cannot be used.